The aim of this application is the elucidation of the roles of potential key elements in mechanisms of synaptic vesicle fusion, recycling and synaptic remodeling. This will be accomplished with two sets of studies connected by their involvement in the membrane traffic of synaptic terminals. The first set of studies focuses on the interaction between the synaptic vesicle protein, synaptotagmin, and the presynaptic proteins, the neurexins, as a mechanism for docking and fusion. The second set of studies focuses on two novel proteins of 47 and 49 kD that bind a snake venom toxin, taipoxin, that blocks synaptic vesicle recycling. The investigators hypothesize that these two proteins are directly involved with uptake of synaptic material that may be part of a mechanism for synaptic remodeling.